1. Field of the Invention
The present invention relates to a method and an apparatus for controlling the fuel injection of an internal combustion engine by air-fuel ratio feedback correction.
2. Description of the Related Art
The air-fuel ratio feedback control technique, wherein an air-fuel ratio feedback correction coefficient is calculated in accordance with detection signals from a concentration sensor for detecting the concentration of a specific component in the exhaust gas, for example, an oxygen concentration sensor for detecting the concentration of the oxygen component (below, "O.sub.2 sensor"), and using this correction coefficient to correct the fuel injection to the engine so as to control the engine air-fuel ratio to the desired value, is well known. By such air-fuel ratio feedback control, the air-fuel ratio state of the exhaust gas flowing into the 3-way catalytic converter is adjusted and the exhaust gas cleaning characteristics controlled to the most appropriate values.
When such air-fuel ratio feedback control is effected, there is a variable frequency and amplitude of the air-fuel ratio feedback correction coefficient maximizing the cleaning characteristics of the 3-way catalyst. However, the feedback frequency and amplitude of the air-fuel ratio correction coefficient change in accordance with the exhaust gas flow at that time. In the prior art, this feedback control frequency and amplitude have not been controlled at all, and therefore, it has not been possible to maintain the cleaning performance at its maximum level under all running conditions.